Nickel or nickel compounds are widely used as catalysts for chemical synthesis such as in oxidation reactions, reduction reactions, hydrogenation reactions or the like. Conventional examples of the use of nickel or nickel compounds in oxidation reactions may include: (1) an alcohol oxidation reaction in which nickel peroxide (NiO2) is used as a stoichiometric oxidizing agent (Non-Patent Document 1), (2) an alcohol aerobic oxidation reaction using Ni—Al hydrotalcite as a catalyst (Non-Patent Document 2), (3) an alcohol aerobic oxidation reaction using Mg—Al hydrotalcite containing Ni(II) as a catalyst (Non-Patent Document 3), and (4) an alcohol aerobic oxidation reaction using nickel peroxide (NiO2) nanoparticles as a catalyst (Non-Patent Document 4).
As described in (1) above, highly oxidized nickel peroxide has a higher level of oxidizing power than nickel oxide, and has long been known to be able to oxidize various alcohols stoichiometrically. This type of nickel peroxide has not been obtained in pure form or in the form of an anhydride, there are many aspects of its structure that remain unclear, and is also said to be a nickel oxide that has adsorbed oxygen. However, since nickel peroxide is extremely useful as a stoichiometric oxidizing agent, if it were possible to catalytically generate active oxidizing active species using moleculer oxygen for the oxidizing agent, it would be able to be applied to aerobic oxidation of numerous organic substrates.
Catalytic alcohol aerobic oxidation reactions have been realized in recent years as a result of various modifications and improvements to nickel-based catalysts. The nickel-hydrotalcite-based catalysts described in (2) and (3) above realize highly efficient activation of moleculer oxygen by compounding Ni with dissimilar metal elements (such as Al or Mg), thereby achieving aerobic oxidation with a heterogeneous nickel catalyst. In these catalysts, Ni functions as an oxygen activation site as a result of compounding Ni with a dissimilar metal element, and is thought to result in the formation of peroxo species serving as reactive species on the Ni. In addition, in the method described in (4) above using nickel peroxide, the reaction has been reported to proceed catalytically as a result of forming the nickel oxide into nanoparticles.
In the chemical industry, the use of nickel and nickel compounds is not limited to alcohol oxidation reactions, but have also been shown to be widely effective in various reactions such as various oxidation reactions, reduction reactions and hydrogenation reactions, as well as in catalysts for purification of automobile exhaust gas and in photocatalysts.    Non-Patent Document 1: J. Org. Chem., 27 (1962) 1597    Non-Patent Document 2: Angew. Chem. Int. Ed., 40 (2001) 763    Non-Patent Document 3: J. Mol. Catal., A236 (2005) 206    Non-Patent Document 4: Appl. Catal., A282 (2005) 25